I've got another update, again just for the sake of helping anyone else who comes along with similar problems.
So, I left off above with buying a new hard drive and reinstalling the OS on that drive (misconception/problem #1) to get the PC up and running again, with the assumption being that the old hard drive was basically done in and not trustworthy (misconception/problem #2), if not totally shot. I had a backup of my data from an external USB hard drive that I faithfully wrote backups to every night using the Windows backup utility, so I was 'secure' on that score (misconception/problem #3.)
First, let me address the misconceptions, then I'll go on to how it was all fixed and I got to my happy ending.
Misconception/problem #1: reinstalling the OS.
I've done this on other machines before and it never seemed like a big deal. Not so on the XPS 630i. Well, installing an OS on a new drive is not a big deal, but it will be nothing like the old computer you had, being as it's not at all 'Delled." It's just a drone. But the 630i is a rather highly tweaked machine, so getting it back to that state would be horrific. (I've since seen the guides and driver links and whatnot here, and while that's great, basically, if you can avoid it, that's the way to go. Dell itself has guides on how to re-Dell your OS, but as usual they're fairly cryptic, and being as I had Windows XP and needed to keep it for various audio hardware compatibility reasons, I also had to deal with the constant red-headed stepchild attitude coming from every corner - XP links inexplicably changing to Win7 or 8 references, grim "WinXP is no longer supported" reminders, etc.) Complicating all this was the fact that the base OS reinstall wouldn't make use of the ethernet adapter without a proper driver, so I couldn't get online with that machine to do anything. Luckily I had the cheap laptop I just bought as a stopgap measure to do that. Special note:
you basically need an internet-connected second computer right there if you're hoping to accomplish anything in a timely fashion.Funny/unbelievable sidenote:
Dell literally has a troubleshooter for diagnosing connectivity issues that requires connectivity to use. It's not something you can download on another machine and copy over and install, as it requires an interface with the affected machine. So in order to use the utility, you have to be able to do the thing that the utility is supposed to try to discover why you can't do.
Misconception/problem #2: the old drive was not shot. I was able to hook up the drive to another computer and look it over, and everything seemed fine structurally. All my data was still there and accessible. I couldn't find any damaged sectors or anything like that. The only problem was that it wouldn't boot. Or so I thought. After the new OS debacle, I was desperate not to go down that road so I attempted to boot the old OS from the old drive, and eventually I was able to in safe mode. It would only work without networking though, and the boot always hung at something called avgidshx.sys. I later found that this is a file having to do with AntiVirus Guard (AVG) which can, ironically, interfere/disable internet connectivity if it's corrupted. Anyway, it would eventually boot despite that hang, and in safe mode I was able to do a system restore to a date before the power surge. This allowed me to boot up in normal mode again, so all of sudden things weren't looking so dire. I was back in my old system. I was able to restore limited connectivity by reinstalling the Dell/nVidia ethernet adapter driver, but the system was still struggling, and I'd frequently get a variety of BSODs - stuff like PAGE_FAULT_IN_NONPAGED_AREA and kernal errors and IRQL_LESS messages - which mostly tended to point to memory issues in my searches. At any rate, the hard drive was not shot, and the data on it was intact, which was a good thing because ...
Misconception/problem #3: Windows backup utility. Ironically, while my data on the system drive was intact, the backup data was not. This could be because the process was interrupted when I shut off the computer that fateful morning (it was running at the time), but whatever the reason, I had about two thirds of it, in the cryptic and and I later discovered not-highly-regarded .bkf format. Basically nothing or very little besides Windows Backup can actually read a .bkf file. I won't get into it here, but do not use Windows Backup for backups
. Just don't. There's much better out there.
Onto the happy ending ...
First of all I uninstalled AVG, and even used a utility called AVG Remover to get rid of all traces of AVG from the registry. This cleared up the boot issues. The system seemed happier and was good with connectivity again. I also updated all the drivers I could get my hands on through Dell for my specific equipment. That left figuring out the persistent BSODs. Focusing on memory, I used memtest86 to test all my remaining sticks individually, letting the utility do three passes on each stick. They all passed. I then put my bad stick in just to see what it would do, and the long-beep/two shorter beeps failure returned, so that was definitely due to that bad stick. I took it back out and all was well again. Then the most important thing: I read somewhere that sometimes simply moving the RAM modules around into different slots can resolve memory issues. I did that, and I haven't had a BSOD since. That was only a day or so ago, and I'm still watchful, but the system does seem happy. (You know that feeling where you know something's wrong, and the same feeling where you know everything feels right.)
Next thing was to run all the available Dell diagnostics for my system, now that I was connected again. Dell has a very handy utility for doing this, and all my stuff passed.
Last thing was that my old drive, healthy as it remained, was almost full, so I figured now was a good time to move the OS since I had the new drive sitting there doing nothing. So I wiped the reinstalled OS off it it and got clone/backup software from Acronis. They have some free varieties for owners of certain manufacturer hard drives, and WD was one, which is the brand of the drive I bought. I used this to clone the old drive onto the new drive and it worked like a charm. The software interface is very user friendly so the procedure was easy (as opposed to the frequently cryptic nature of this stuff). It even changed the drive letter of the new OS drive to C: for me.
After that it's been just a matter of housekeeping - getting the latest Windows updates, reinstalling AVG (the software itself isn't evil, just when something gets corrupted), and defragmenting my hard drive(s). I left it all on overnight and everything was stable in the morning, with no BSODs or other issues. (I'd awoken to one the morning before.)
So, the main takeaways:
1. If you suffer a power surge, don't automatically assume your PSU or mobo took the hit. It could be something else, like RAM in my case.
2. Don't try to reinstall Windows XP on anything but a budget Dell if you can help it. Recreating the actual Dell system will be a nightmare.
3. Don't use the Windows Backup utility for backups. Use something else. I recommend Acronis software. It worked great for cloning in my case, and while I haven't used it for backups yet, I assume that if it can handle cloning, it can handle backups.
4. I'd suggest doing frequent system state backups onto removeable media in addition to data backups. This will ensure that if the OS goes belly up due to hard drive failure or something like that, you'll be in a good position to restore the life you had the day before. Acronis does that as well.
Thanks to My630.com btw - it was good to find a port in the storm like this during the crisis.